Vinh is the founder of the widely read Basam [1]blog, which publishes highlights of local press as well as dissident tracts critical of the government.

Basam and its US-based managing editor Ngoc Thu have been repeatedly targeted by hackers with suspected links to the Vietnam state over the last 18 months. She said the arrests were “groundless” and insisted that the struggle for basic democratic freedoms in the country would continue.

“Dissident bloggers can be arrested, blogs can be shut down, but they are like wild grass with deep roots that can’t be dug up,” she wrote in a posting on the blog on Tuesday. “The government cannot control information on the internet, because no one can control the thoughts of other people.”

“Dissident bloggers can be arrested, blogs can be shut down, but they are like wild grass with deep roots that can’t be dug up.”

Ngoc Thu

Vinh, 58, was a regular on anti-China protests in the capital. At a recent one, he wore a camera fitted to his head to record the action and publish it online later.

He was formerly a security police officer. In 1999, he quit and started one of Vietnam’s first private detective agencies. His father was a former labour minister and ambassador to the Soviet Union.

Vietnam’s authoritarian government is under international pressure to respect basic human rights such as free speech and political assembly, but still maintains a tight grip on its citizens. The emergence of the internet over the past five years has opened up new avenues for political dissent and organisation, spooking the country’s rulers.

The arrests of the two bloggers were the first reported since June last year. Verdicts against others who had been arrested before have been handed down, and harassment and sometime violent attacks on dissidents have increased over the past year, according to activists and diplomats monitoring the situation.

Last month, the government granted early release to three dissidents, one of which flew directly from prison to the United States, which brokered a deal to secure his release. The unusual move was seen by some as a ploy to help ease ongoing trade negotiations between Hanoi and Washington, which has said that progress on the deal – the-Trans Pacific Partnership – would be hard without human rights improvements.

New York-based Human Rights Watch says that the number of people sentenced in political trials in Vietnam has increased every year since 2010, and that at least 63 people were imprisoned for peaceful political expression last year.